What oclHashcat really does is update the restore point as soon as it is safe to do so: mark the keyspace unit (KU) as done if and only if it is (completely) done.
It cannot mark it as done when the current keyspace unit (CURKU) is not finished yet (otherwise it could happen that it skips keyspace and some hashes that should crack do not).

Definitely happens exactly as magnum has outlined. I lost quite a few sessions due to this while learning oclhashcat so it's not just v1.37 that's affected. Dunno why I never thought to raise it in trac though. Sorry about that.